Electrically conductive polyethylene resin composition, electrically conductive polyethylene resin molding, sliding bearing, and sliding sheet

ABSTRACT

The present invention provides an electrically conductive polyethylene resin composition having a stable volume resistance value and in addition, a low-friction property and a wear-resistant property and a resin molding, a sliding bearing, and a sliding sheet made of the electrically conductive polyethylene resin composition. The electrically conductive polyethylene resin composition contains 100 parts by weight of ultra-high-molecular-weight polyethylene resin which cannot be injection-molded and has a weight average molecular weight of one million to four millions, 2 to 15 parts by weight of Ketjenblack, and 0.5 to 5 parts by weight of at least one powder, having an average particle size of 1 to 30 μm, which is selected from among polytetrafluoroethylene resin powder, graphite powder, and silicone resin powder.

RELATED APPLICATION

This application claims foreign priority from of Japanese PatentApplication No. 2009-220666, filed Sep. 25, 2009, and also claimspriority from Japanese Patent Application No. 2008-253851, filed Sep.30, 2008, which are incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an electrically conductive polyethyleneresin composition and a resin molding, a sliding bearing, and a slidingsheet composed of the electrically conductive polyethylene resincomposition.

BACKGROUND ART

Electrically conductive resin compositions are widespread in industryand utilized for various uses and particularly for uses requiringelectrical conductivity. As the electrically conductive resincompositions, various compositions each containing resin and a largeamount of an electrically conductive filler such as carbon black addedthereto are known. Because the electrically conductive resincompositions are economically excellent, they are widely utilized mainlyin industry.

In recent years, electrically conductive polymer materials have spreadin packaging industry of IC chips, and a variation of the electricallyconductive polymer materials is diversified from general-purposeplastics to engineering plastics. It has become increasingly importantto take measures for controlling the electrical conductivity ofprecision equipment and those of peripheral devices disposed on theperiphery thereof. As electrically conductive fillers for theelectrically conductive polymer materials, in addition to carbon black,carbon fibers, graphite, metal coating fillers, metal fibers, and thelike are used widely and properly in dependence on purposes andfunctions. But the electrically conductive fillers have problems thatthey deteriorate mechanical properties of the polymer materials andcause moldability to be difficult.

Polyethylene (hereinafter referred to as PE) resin is excellent in itsfriction and wear properties and mechanical strength and thus widelyapplied. In addition, an electrically conductive PE resin compositioncontaining the electrically conductive filler has also widely spread. Inrecent years, with the spread of the precision equipment, a higherelectrical conductivity control function is demanded, and thus lowfriction and wear properties and a stable electrical conductivity aredemanded more than ever. A complex composed of the PE resin and theelectrically conductive filler represented by carbon black has excellentelectrical conductivity and is thus effective for applications requiringelectrical conductivity.

For example, an electrically conductive complex composed ofultra-high-molecular-weight polyethylene (hereinafter referred to asUHMWPE) and granular glassy carbon is known (see patent document 1). Theelectrically conductive complex has a positive characteristictemperature coefficient showing a very large maximum change rate ofresistance in a very narrow temperature range.

An electrically conductive thermoplastic resin composition containing100 parts by weight of PE-based resin having a density of 0.84 to 0.90g/cm³ and 50 to 1000 parts by weight of a metal filler and/or carbonblack is also known (see patent document 2). The electrically conductivethermoplastic resin composition is excellent in molding processabilitysuch as in injection molding processability.

An electrically semi-conductive UHMWPE composition, having a specificvolume resistivity of 10⁵ to 10⁹ Ω·cm, which contains the UHMWPE havinga weight average molecular weight of not less than 5.0×10⁵ and apolydispersity degree in the range of 15 to 100 and Ketjenblackdispersed in the UHMWPE is also known (see patent document 3). At thetime of the production of the electrically semi-conductive UHMWPEcomposition, the UHMWPE and the Ketjenblack are fused and kneaded byusing a screw extruder.

PRIOR ART DOCUMENT Patent Document

Patent document 1: Japanese Patent Application Laid-Open No. 7-94018

Patent document 2: Japanese Patent Application Laid-Open No. 10-251459

Patent document 3: Japanese Patent Application Laid-Open No. 2008-138134

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

But the electrically conductive complex disclosed in the patent document1 has the positive characteristic temperature coefficient showing a verylarge maximum change rate of resistance in the very narrow temperaturerange of 125 to 140° C. Therefore the electrically conductive complex isused only for a fuse and a planar heating element and is thusunversatile in its use. It is very difficult to use the electricallyconductive complex for a sliding bearing.

Because the electrically conductive thermoplastic resin compositiondisclosed in the patent document 2 contains the metal filler having aspecific gravity not less than four times larger than that of the baseresin, it is difficult to uniformly mix the base resin and the metalfiller with each other. Thus there is a variation in its conductivity.Further the carbon black has a bulk density much smaller than that ofthe base resin. Therefore when as large as 50 parts by weight of thecarbon black is added to 100 parts by weight of the base resin, it isdifficult to uniformly mix the base resin and the carbon black with eachother. Thus there is a variation in the conductivity of the electricallyconductive thermoplastic resin composition.

In the electrically semi-conductive UHMWPE composition disclosed in thepatent document 3, the UHMWPE resin (UHMWPE resin which can beinjection-molded) which can be fused and kneaded with the electricallyconductive filler by using the screw extruder is adopted as the baseresin. Such UHMWPE resin has a low-friction property, but has aninsufficient wear resistance.

The present invention has been made to cope with the above-describedproblems. It is an object of the present invention to provide a resincomposition having conductivity in a degree not so high or intermediate(for example, volume resistance value: 1.0×10⁴ to 1.0×10¹⁰ Ωcm) and moreparticularly an electrically conductive PE resin composition having astable volume resistance value and in addition, a low-friction propertyand a wear-resistant property and a resin molding, a sliding bearing,and a sliding sheet made of the electrically conductive PE resincomposition.

Means for Solving the Problem

The electrically conductive PE resin composition of the presentinvention is composed of 100 parts by weight of UHMWPE resin whichcannot be injection-molded, 2 to 15 parts by weight of electricallyconductive carbon, and 0.5 to 5 parts by weight of at least one powderselected from among polytetrafluoroethylene (hereinafter referred to asPTFE) resin powder, graphite powder, and silicone resin powder.

Regarding ingredients of the electrically conductive PE resincomposition, the UHMWPE resin which cannot be injection-molded is UHMWPEresin having a weight average molecular weight of one million to fourmillions. Particles of the UHMWPE resin which cannot be injection-moldedare unspherical.

An average particle size of the UHMWPE resin which cannot beinjection-molded is not less than three times larger than that of theelectrically conductive carbon and that of the powders. The averageparticle size of the UHMWPE resin which cannot be injection-molded is100 to 200 μm. The average particle size of the electrically conductivecarbon is not more than 1 μm. The average particle size of the powdersis 1 to 30 μm. The electrically conductive carbon is Ketjenblack.

The electrically conductive PE resin molding of the present invention isformed by compression-molding the electrically conductive polyethyleneresin composition and has a volume resistance value of 1.0×10⁴ to1.0×10¹⁰ Ωcm. On a surface of the electrically conductive PE resinmolding, the electrically conductive carbon and at least one powderselected from among the PTFE resin powder, the graphite powder, and thesilicone resin powder are disposed at grain boundaries of the particlesof the UHMWPE resin.

The sliding bearing of the present invention is made of the electricallyconductive PE resin molding. The sliding bearing is a plain bearing. Theplain bearing means a bearing which, inclusive of a sliding surface, isentirely integrally formed with the same material. The sliding bearingis a lamination sliding bearing bonded to a back metal.

The sliding sheet of the present invention is formed by performing acutting work on the electrically conductive PE resin molding.

Effect of the Invention

The electrically conductive PE resin composition of the presentinvention contains 100 parts by weight of the UHMWPE which cannot beinjection-molded, 2 to 15 parts by weight of the electrically conductivecarbon, and 0.5 to 5 parts by weight of at least one powder selectedfrom among the PTFE resin powder, the graphite powder, and the siliconeresin powder. Therefore by compression-molding the electricallyconductive PE resin composition, a molding having a uniform and stablevolume resistance value is obtained.

Because the UHMWPE resin which cannot be injection-molded is UHMWPEresin having a weight average molecular weight of one million to fourmillions, the molding having a uniform and stable volume resistancevalue, a low-friction property, and a wear-resistant property isobtained. Because the particles of the UHMWPE resin which cannot beinjection-molded are unspherical, the particles of the UHMWPE resinwhich cannot be injection-molded easily contact each other and are thuseasily fused to each other in compression molding. Therefore the moldinghas a high mechanical strength.

Because the average particle size of the particles of the UHMWPE resinwhich cannot be injection-molded is not less than three times largerthan those of the other ingredients, the particles of the otheringredients easily adhere to those of the UHMWPE resin which cannot beinjection-molded. Therefore the ingredients are capable of easilydisplaying the properties thereof. Because the average particle size ofthe particles of the UHMWPE resin which cannot be injection-molded is100 to 200 μm, that of the electrically conductive carbon is not morethan 1 μm, and that of the powders is 1 to 30 μm, the ingredients arecapable of easily displaying the properties thereof to a higher extent.

The electrically conductive PE resin molding has the volume resistancevalue of 1.0×10⁴ to 1.0×10¹⁰ Ωcm. On at least the surface of themolding, the electrically conductive carbon and at least one powderselected from among the PTFE resin powder, the graphite powder, and thesilicone resin powder are disposed at the grain boundaries of theparticles of the UHMWPE resin. Because the molding has theabove-described structure, it is possible to preferably use the moldingfor applications requiring intermediate electrical conductivity. Any ofa plain-type sliding bearing obtained by molding the electricallyconductive PE resin composition, a lamination-type sliding bearing inwhich a sheet-shaped sliding sheet obtained by processing theelectrically conductive PE resin composition is bonded to a back metal,and a sliding sheet obtained by processing the electrically conductivePE resin composition is excellent in the stability of the volumeresistance value, the low-friction property, and the wear-resistantproperty.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a plain-type sliding bearing to beobtained by molding an electrically conductive PE resin composition ofthe present invention.

FIG. 2 is a perspective view of a lamination-type sliding bearingcomposed of a sliding sheet processed into the shape of a sheet from theelectrically conductive PE resin composition of the present inventionand a back metal to which the sliding sheet is bonded.

FIG. 3 shows a change of the friction coefficient of the electricallyconductive PE resin composition of the present invention with time.

FIG. 4 shows a wear depth of the electrically conductive PE resincomposition of the present invention.

FIG. 5 is an enlarged photograph of the surface of a molding of anexample 2 and a schematic view thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

The base resin of the electrically conductive PE resin composition ofthe present invention is UHMWPE resin which cannot be injection-molded.The UHMWPE resin is PE resin to be obtained by increasing the molecularweight of PE resin which is crystalline thermoplastic resin obtained bypolymerizing ethylene to 500,000 to 7,000,000 from 20,000 to 300,000which is the normal molecular weight of the PE resin. The UHMWPE resinhas unadhesiveness, a low-friction property, and a high insulationproperty and is easily electrostatically charged. Because the UHMWPEresin has improved wear-resistant property and excellent low-frictionproperty, the UHMWPE resin is used as a material of a sliding bearing.But the UHMWPE resin having a molecular weight more than a million has avery high viscosity when it melts and thus hardly flows. Therefore it isvery difficult to mold such UHMWPE resin by a normal injection-moldingmethod. Thus after a material of such UHMWPE is molded by compressionmolding or RAM extrusion molding, the material is mechanically processedinto a desired configuration. The UHMWPE resin which cannot beinjection-molded has a lower frictional property than UHMWPE resin whichcan be injection-molded and is excellent in its wear resistance.

The UHMWPE resin that can be used in the present invention is powder ofthe UHMWPE resin having a weight average molecular weight of one millionto four millions. The UHMWPE resin powders having a commercial name ofHI-ZEX MILLION (weight average molecular weight: 500,000 to 6,000,000)and MIPELON (weight average molecular weight: 2,000,000) produced byMitsui Chemicals, Inc. are exemplified.

It is desirable that particles of the UHMWPE resin which cannot beinjection-molded are unspherical. It is desirable that the unsphericalparticles thereof do not have a particular configuration, but havedifferent configurations. In compression-molding the UHMWPE resin havingdifferent configurations, the particles of the UHMWPE resin havingdifferent configurations contact each other to a high extent, eventhough ingredients are added to the UHMWPE resin which cannot beinjection-molded and thus the particles easily fuse to each other.Thereby a molding has a high mechanical strength such as its tensilestrength and flexural strength and excellent wear resistance.

When the average particle size of the particles of the UHMWPE resinwhich cannot be injection-molded is not less than three times largerthan those of other ingredients, the ingredients are capable of easilypenetrating gaps between the particles of the UHMWPE resin, and at thesame time the particles of the UHMWPE resin are capable of contactingone another. Thereby the ingredients are capable of easily displayingthe properties thereof without deteriorating the mechanical strength andwear resistance of the molding. As specific ranges of the averageparticle sizes of the ingredients of the electrically conductive PEresin composition, it is preferable that the average particle size ofthe particles of the UHMWPE resin which cannot be injection-molded is100 to 200 μm, that the average particle size of electrically conductivecarbon is not more than 1 μm, and that the average particle size ofparticles of powders is 1 to 30 μm, because the electrically conductivecarbon and the powders which are the ingredients of the electricallyconductive PE resin composition are easily capable of displaying theproperties thereof to a higher extent. The average particle sizes aremeasured by a laser analytical method. As a laser analysis granularitydistribution measuring device, it is possible to use Microtrac HRAproduced by Leeds and Northrup Co.

Electrical conductivity is imparted to the electrically conductive PEresin composition by adding the electrically conductive carbon to theUHMWPE resin which cannot be injection-molded. As the electricallyconductive carbon, it is possible to use any of carbon fibers, carbonnanotubes, fullerene, and carbon powder. Of these electricallyconductive carbons, the carbon powder is preferable because it does nothave configuration anisotropy and is excellent in its cost performance.Carbon black is known as the carbon powder. It is possible to use thecarbon black produced by any of a decomposition method such as a thermalblack method and an acetylene black method; and an incomplete combustionmethod such as a channel black method, a gas furnace black method, anoil furnace black method, a pine smoke method, and a lamp black method.From the standpoint of electrical conductivity, furnace black, acetyleneblack, and Ketjenblack (registered trademark) are favorably used. Ofthese carbon blacks, the Ketjenblack is more favorable than the furnaceblack and the acetylene black because the Ketjenblack is excellent inits conductivity.

It is preferable that the primary particle size of the Ketjenblack is 30to 38 nm. When the primary particle size thereof is in this range, theelectrically conductive PE resin composition is capable of obtaining asufficient volume resistivity, even though it contains a small amount ofthe Ketjenblack. The BET specific surface area of the Ketjenblack ispreferably 1000 to 1500 m²/g. When the specific surface area thereof isin this range, the stability of the volume resistivity is excellent,even though the electrically conductive PE resin composition contains asmall amount of the Ketjenblack. As such Ketjenblack, KetjenblackEC-600JD produced by Akzo Nobel Polymer Chemicals LLC is exemplified.

The electrically conductive PE resin composition of the presentinvention contains the UHMWPE resin which cannot be injection-molded andto which the electrically conductive carbon, and at least one powder,selected from among the PTFE resin powder, the graphite powder, and thesilicone resin powder are added. These powders serve as a lubricityimparting material for imparting lubricity to the molding to beobtained. By adding these powders to the UHMWPE resin which cannot beinjection-molded, the low-friction property of the electricallyconductive resin composition is stabilized. In addition, by adding theselubricity imparting materials to the UHMWPE resin which cannot beinjection-molded, the electrically conductive carbon easily disperses atthe interface of the particles of the UHMWPE resin which cannot beinjection-molded, and the stability of the volume resistivity isexcellent, even though the addition amount of the carbon is small.

To allow the stabilization of the low-friction property of theelectrically conductive PE resin composition of the present invention tobe excellent, it is preferable that the average particle size of each ofthe above-described powders is 1 to 30 μm.

As the PTFE resin powder, powder for molding use and powder for a solidlubricant can be used. The PTFE resin powder modified with alkyl vinylether is preferable because such PTFE resin powder enhances the wearresistance of the electrically conductive PE resin composition.

The graphite powder is classified into natural graphite and artificialgraphite. The artificial graphite is unsuitable as a lubricant becausethe lubrication performance thereof is inhibited by carborundum formedwhile the artificial graphite is being produced and because it isdifficult to produce sufficiently graphitized graphite. Because thenatural graphite is produced in a perfectly graphitized state, it has avery high lubrication performance and is thus suitable as the solidlubricant. But the natural graphite contains a large amount ofimpurities which deteriorate its lubrication performance. Thus it isnecessary to remove the impurities. But it is difficult to completelyremove them.

The graphite powder preferable in the present invention is theartificial graphite containing not less than 98.5 wt % of fixed carbon,because such artificial graphite allows the electrically conductive PEresin composition to easily obtain stable low-friction property.

The silicone resin powder can be preferably used because sphericalsilicone resin is excellent in the stability of the low-frictionproperty of the electrically conductive PE resin composition. Thesilicone resin powder of the present invention consists of amethylsilsesquioxane unit and a phenylsilsesquioxane unit or thephenylsilsesquioxane unit. The methylsilsesquioxane unit is shown by(CH₃) SiO_(3/2). The phenylsilsesquioxane unit is shown by(C₆H₅)SiO_(3/2). The silicone resin powder may contain a small amount of(CH₃)₂(C₆H₅)SiO_(1/2), (CH₃)₃SiO_(1/2), (CH₆H₅)₃SiO_(1/2),(CH₃)(C₆H₅)₂SiO_(1/2), (CH₃)₂SiO_(2/2), (C₆H₅)₂SiO_(2/2), (CH₃)(C₆H₅)SiO_(2/2), and SiO_(4/2). The spherical silicone resin has a property ofpreventing the deterioration of the wear resistance of the electricallyconductive PE resin composition.

Regarding the mixing ratio of the components of the electricallyconductive PE resin composition, 2 to 15 parts by weight of theelectrically conductive carbon and 0.5 to 5 parts by weight of at leastone powder selected from among the PTFE resin powder, the graphitepowder, and the silicone resin powder are added to 100 parts by weightof the UHMWPE resin which cannot be injection-molded.

When the mixing ratio of the electrically conductive carbon is in therange of 2 to 15 parts by weight, the electrically conductive PE resincomposition is capable of having the volume resistance value of 1.0×10⁴to 1.0×10¹⁰ Ωcm. When the mixing ratio of the electrically conductivecarbon is less than two parts by weight, the electrically conductive PEresin composition is capable of obtaining the volume resistance value of1.0×10¹⁰ Ωcm, whereas when the mixing ratio of the electricallyconductive carbon exceeds 15 parts by weight, the moldability of theelectrically conductive PE resin composition is inferior.

When the mixing ratio of the PTFE resin powder, the graphite powder,and/or the silicone resin powder is less than 0.5 parts by weight, theelectrically conductive PE resin composition is incapable of obtainingthe low-friction property, and the stability of the low-frictionproperty is inferior. When the mixing ratio of the PTFE resin powder,the graphite powder, and/or the silicone resin powder exceeds 5 parts byweight, the electrically conductive PE resin composition may haveinferior wear resistance.

On the surface of the electrically conductive PE resin molding of thepresent invention, the electrically conductive carbon and the powdersserving as the lubricity imparting material are disposed at grainboundaries of the particles of the UHMWPE resin which cannot beinjection-molded. The electrically conductive carbon is uniformlydispersed at the grain boundaries owing to the action of the lubricityimparting material. Thereby the electrically conductive PE resin moldingis capable of having the volume resistance value of 1.0×10⁴ to 1.0×10¹⁰Ωcm.

Because the electrically conductive PE resin molding of the presentinvention has the volume resistance value of 1.0×10⁴ to 1.0×10¹⁰ Ωcm andexcellent friction and wear resistance, it is possible to preferably usethe electrically conductive PE resin molding for application requiringintermediate electrical conductivity. For example, any of a plain-typesliding bearing obtained by molding the electrically conductive PE resincomposition, a lamination-type sliding bearing in which a sheet-shapedsliding sheet obtained by processing the electrically conductive PEresin composition is bonded to a back metal, and a sliding sheetobtained by processing the electrically conductive PE resin compositionis excellent in the stability of the volume resistance value thereof,the low-friction property, and the wear-resistant property thereof.

When the electrically conductive PE resin composition is molded into asheet having a thickness of 0.04 to 1.0 mm, the obtained sheet has anexcellent stability in its volume resistance value and in low-frictionproperty and wear-resistant property. Therefore the obtained sheet canbe preferably used as various static electricity elimination sheets orelectrically conductive sheets.

Various products made of the electrically conductive PE resincomposition of the present invention can be produced by carrying out thefollowing producing method: After each of the components including theparticles of the UHMWPE resin which cannot be injection-molded, theelectrically conductive carbon, the PTFE resin powder, the graphitepowder and/or the silicone resin powder is weighed, a homogeneousmixture is prepared. The homogeneous mixture is supplied to a moldingdie to mold it into a billet which is a material to be molded bycompression molding including preforming, calcining, and main molding.The billet is mechanically processed into desired various configurationsof products. To process the billet into a sheet, the billet is attachedto a lathe and subjected to skiving processing like radish skivingperformed to use skived radish as garnishing for raw fish.

It is possible to mold the electrically conductive PE resin compositioninto a round bar or a tube material by means of ram continuous extrusionmolding. These materials are processed into various configurations ofproducts by machining. For example, these materials can be processedinto a bush (cylindrical bearing) shown in FIG. 1.

Because various products made of the electrically conductive PE resincomposition obtained in this manner have stable conductivity,low-friction property, and excellent wear-resistant property, they canbe used as a sliding bearing. Because such products have excellentwear-resistant property for surfaces of mating materials having a highextent of roughness, various products made of the electricallyconductive PE resin composition can be used as the sliding bearingapplicable outdoors and to environment in which powder is used. Thesliding bearing obtained from the electrically conductive PE resincomposition of the present invention does not contain a hard material.Thus even though the mating material is a soft material made ofsynthetic resin, aluminum, alloys thereof, copper, and alloys thereof,the sliding bearing does not wear the mating material.

Embodiments of the sliding bearing of the present invention aredescribed below with reference to FIGS. 1 and 2. As shown in FIG. 1, thesliding bearing made of the electrically conductive PE resin compositionof the present invention can be used as a plain-type sliding bearing 1cut out of the billet produced by means of the compression molding. Asshown in FIG. 2, a sliding sheet 3 processed into the shape of a sheetfrom the electrically conductive PE resin composition of the presentinvention can be used as a lamination-type sliding bearing 1 stuck to aback metal 2. The lamination-type sliding bearing, shown in FIG. 2,having the back metal has a merit that the amount of the electricallyconductive PE resin composition to be used therefor is smaller than theamount thereof to be used for the plain bearing shown in FIG. 1 and thatthe lamination-type sliding bearing can be used at a higher surfacepressure than the plain bearing.

The sliding bearing obtained by molding the electrically conductive PEresin composition of the present invention can be used as variousbearings such as a guide roller for guiding a tape and a rail, a radialbearing and a thrust bearing supporting a supporting shaft, and agrounding button from which it is necessary to eliminate staticelectricity.

Further, because the sliding bearing obtained by molding theelectrically conductive PE resin composition is excellent in itsflexibility, it can be used by shaping it in the form of a plate or asheet with the sliding bearing being flexed. Because the sliding bearingcan be used with the sliding bearing being flexed, the sliding bearingis capable of closely contacting a portion from which static electricityis required to be eliminated and reliably eliminating the staticelectricity.

The sliding sheet made of the electrically conductive PE resincomposition of the present invention can be used as various electricallyconductive sheets or static electricity elimination sheets such as athrust washer, an electromagnetic wave shield, a static electricityelimination sheet of a car, an IC package, an electrode lead wire, agrounding material of a pump.

EXAMPLES

Materials used in examples and comparative examples are shown below.Mixing ratios are shown in table 1.

(1) UHMWPE resin which cannot be injection-molded—1: HI-ZEX MILLION 24OSproduced by Mitsui Chemicals, Inc., weight average molecular weight: twomillions, average particle size measured by laser analytical method: 120μm, particles having different configurations (like baron potato)(2) UHMWPE resin which cannot be injection-molded—2: HI-ZEX MILLION 240Mproduced by Mitsui Chemicals, Inc., weight average molecular weight: 2.4millions, average particle size measured by laser analytical method:1600 μm, particles having different configurations (like baron potato)(3) Electrically conductive carbon: Ketjenblack EC-600JD produced byAkzo Nobel Polymer Chemicals LLC, primary particle size: 34 nm (averageparticle size measured by laser analytical method: not more than 0.5μm), BET specific surface area: 1270 m²/g.(4) PTFE resin powder: KTL-610 produced by KITAMURA LIMITED, averageparticle size measured by laser analytical method: 12 μm(5) Graphite powder: TIMREX KS-25 produced by Timcal Graphite and CarbonCo., Ltd., fixed carbon: 99.9 wt %, average particle size measured bylaser analytical method: 25 μm(6) Silicone resin powder: KMP-590 produced by Shin-Etsu Chemical Co.,Ltd., average particle size measured by laser analytical method: 2 μm(7) UHMWPE resin which can be injection-molded: LUBMER produced byMitsui Chemicals, Inc., weight average molecular weight: 250,000 to600,000.(8) Polyether ether ketone resin: PEEK-450P produced by Victrex MC Ltd.

Examples 1 Through 4 and Comparative Example 1

At the mixing ratios shown in table 1, the materials were dry-blended byusing a Henschel dry mixer, and a pressure of 0.5 MPa was applied to amixture thereof by using a press machine to preform cylindrical,materials to be processed, each of which had an outer diameter of φ122mm, an inner diameter of 64φ mm, and a height of 100 mm. Thereafter thematerials to be processed were calcined at 370° C. for five hours. Thecalcined cylindrical materials to be processed were subjected to skivingprocessing to obtain sheet materials (molding) each having a thicknessof 1 mm. Specimens each having a length of 30 mm and a side of 10 mmwere cut out of the sheet materials.

Comparative Examples 2 and 3

At the mixing ratios shown in table 1, the materials were dry-blended byusing the Henschel dry mixer. Pellets were produced by using a two-axismelt extruder. After the pellets were molded into cylindrical materials,to be processed, which had a diameter of 40 mm and a length of 10 mm byusing an injection molding machine, the cylindrical materials to beprocessed were subjected to a cutting work to prepare specimens eachhaving a thickness of 1 mm, a length of 30 mm, and a side of 10 mm.

By using the specimens, a friction and wear test and a conductivity testwere conducted. FIGS. 3 and 4 show the results of the friction and weartest. Table 1 shows the results of the conductivity test. FIG. 5 shows amicrophotograph (×500) of the surface of the specimen of the example 2.

In the friction and wear test, a pin-on-disk type testing machine wasused. As test conditions, carbon steel S45C was used as a matingmaterial, and with each specimen stuck to the surface of a base materialmade of rubber (contact surface of specimen with mating material: tip φ5mm×width 1 mm)), each specimen was subjected to the test for 30 hours bysetting a sliding speed to 30 m/min, a surface pressure to 0.5 MPa, anda surface temperature of the mating material to 50° C. The dynamicfriction coefficient of each specimen was measured every 10 hours, andthe wear depth of each specimen immediately after the test finished wasmeasured.

The conductivity test was conducted in accordance with JIS K6371 tomeasure the volume resistance value (Ωcm) by a voltage and current law.

TABLE 1 Components of resin composition & Example Comparative examplemixing ratios (part by weight) 1 2 3 4 1 2 3 UHMWPE resin which cannotbe 100 100 100 — 100 — — injetion-molded-1 UHMWPE resin which cannot be— — — 100 — — — injetion-molded-2 Electrically conductive carbon 2 5 153 3 5 5 PTFE resin powder 0 2 0 4 0 2 5 Graphite particle 0.5 0 0 0 0 00 Silicone resin powder 0 0 5 0 0 0 0 UHMWPE resin which can be — — — —— 100 — injection-molded Polyether ether ketone resin — — — — — — 100Volume resistance value, ×10⁵ Ωcm 5.3 1.9 0.5 2.3 6.4 2.0 2.3

As shown in FIGS. 3 and 4 and table 1, specimens consisting of themoldings of the embodiments composed of the electrically conductive PEresin composition of the present invention had volume resistance values(JIS K6371) in the range of 1.0×10⁴ to 1.0×10¹⁰ Ωcm, low initialfriction coefficients, small changes in the friction coefficients in the30-hour test run, and satisfied the wear resistance. The specimenconsisting of the molding of the comparative example 1 which did notcontain the lubricity imparting material composing the essentialcomponent of the electrically conductive PE resin composition of thepresent invention had a higher friction coefficient than those of themoldings of the examples with time and was thus unstable in its frictionproperty. The specimens consisting of the moldings of the comparativeexamples 2 and 3 for which resins different from the base resin of theelectrically conductive PE resin composition of the present inventionwere used and the mating materials had larger wear volumes than those ofthe examples.

INDUSTRIAL APPLICABILITY

The molding having a uniform and stable volume resistance value, alow-friction property, and a wear-resistant property is obtained fromthe electrically conductive PE resin composition of the presentinvention. Therefore the molding can be utilized as various bearingssuch as a guide roller for guiding a tape and a rail, a radial bearingand a thrust bearing supporting a supporting shaft, and a groundingbutton from which it is necessary to eliminate static electricity.

EXPLANATION OF REFERENCE SYMBOLS AND NUMERALS

-   1: sliding bearing-   2: back metal-   3: sliding sheet

The invention claimed is:
 1. An electrically conductive polyethyleneresin molding formed by compression-molding an electrically conductivepolyethylene resin composition, wherein said electrically conductivepolyethylene resin composition comprises 100 parts by weight ofultra-high-molecular-weight polyethylene resin which cannot beinjection-molded, 2 to 15 parts by weight of electrically conductivecarbon, and 0.5 to 5 parts by weight of at least one powder selectedfrom among polytetrafluoroethylene resin powder, graphite powder, andsilicone resin powder, and particles of said ultra-high molecular weightpolyethylene resin which cannot be injection-molded are unspherical, andsaid electrically conductive carbon and said powders are disposed atgrain boundaries of said particles of said ultra-high-molecular-weightpolyethylene resin which cannot be injection molded and are unspherical.2. The electrically conductive polyethylene resin molding according toclaim 1, wherein said ultra-high-molecular-weight polyethylene resinwhich cannot be injection-molded is ultra-high-molecular-weightpolyethylene resin having a weight average molecular weight of onemillion to four millions.
 3. The electrically conductive polyethyleneresin molding according to claim 1, wherein an average particle size ofsaid particles of said ultra-high-molecular-weight polyethylene resinwhich cannot be injection-molded is not less than three times largerthan that of said electrically conductive carbon and that of saidpowders.
 4. The electrically conductive polyethylene resin moldingaccording to claim 1, wherein said average particle size of saidparticles of said ultra-high-molecular-weight polyethylene resin whichcannot be injection-molded is 100 to 200 μm; said average particle sizeof said electrically conductive carbon is not more than 1 μm; and saidaverage particle size of said powders is 1 to 30 μm.
 5. The electricallyconductive polyethylene resin molding according to claim 1, wherein saidelectrically conductive carbon is Ketjenblack.
 6. The electricallyconductive polyethylene resin molding according to claim 1, wherein saidpolytetrafluoroethylene resin powder is modified polytetrafluoroethyleneresin powder modified with alkyl vinyl ether.
 7. The electricallyconductive polyethylene resin molding according to claim 1, wherein saidgraphite particle is artificial graphite containing not less than 98.5wt % of fixed carbon.
 8. The electrically conductive polyethylene resinmolding according to claim 1, wherein said silicone resin powder isspherical.
 9. The electrically conductive polyethylene resin moldingaccording to claim 1, which has a volume resistance value of 1.0×104 to1.0×1010 Ωcm.